The present invention relates generally to the manufacture of rubber tires for wheeled vehicles. More particularly, the present invention relates to the applying of a separately formed strip of tread stock to a tire carcass, followed by monitoring of the precision of its application.
In manufacturing tires, the assembly of tire elements is generally completed when a separately formed strip of band of tread stock is attached to a green tire carcass, the tread stock being applied either individually or as a sub-assembly consisting of the belts and the tread stock. The tread stock is typically produced by extruding a continuous strip or band of uncured rubber, the extrusion having a cross-sectional shape that is generally hat-like, in that it includes a relatively massive central portion with thin extremities extending outwardly on either side at the lowermost edge of the stock. The strip or band is cut to suitable lengths for subsequent assembly on a green tire carcass or belt package.
Applying the tread stock to the tire carcass in other than a precisely centered manner results in a non-uniform displacement of rubber during the shaping stage of the curing process. The situation can result in a non-uniform tire. For example, consider a radial ply carcass on which the belts had been properly aligned and assembled. Next, assume that the tread stock is inadvertently applied either off center or in a crooked or wobbly manner. During the shaping or curing process, the mold will force the tread stock material into the proper configuration. This unsymmetric or non-uniform lateral displacement of tread stock material may, during the shaping or curing process, result in a similar but opposite lateral displacement of one or more of the underlying belts. In addition to such lateral displacement of the underlying belts, such off-center or crooked tread stock may also result in uneven distribution of the tread stock on the cured tire structure, causing an undesirable deformation of the underlying tire structure elements and also causing a serious, uncorrectable lateral balance problem. The presence of such conditions in the finished, cured tire could adversely affect the tire's operating characteristics, and upon detection at final inspection, such tires are discarded.
To assist the machine operator in the orientation of the tread stock, a number of complex reference guide means have been developed. For example, U.S. Pat. No. 3,923,390, issued Dec. 2, 1975 to Susko, projects reference lines of light onto the surface of the belt and tread stock package being assembled. The projected lines are generally positioned to coincide with the rounded shoulder areas of the tread stock extrusion. A second example is disclosed in U.S. Pat. No. 3,026,230, issued Mar. 20, 1962 to Nebout.
Following positioning of the tread stock on the tire carcass, the assembled green tire is consolidated by a process called stitching. Stitching is performed by rolling rigid stitcher wheels over the surface of the tire assembly to bring the tacky surfaces of the tread stock and tire carcass into intimate contact and to work out any entrained air.
Even when the tread stock material has been properly positioned on the tire carcass, its position does not become substantially fixed until completion of the stitching operation. Thus, there is also the possibility that properly positioned tread stock can become displaced between application and stitching. For example, in the case of a two-stage radial tire assembly process, the tacky tread material may partially stick to the building drum apparatus or the transfer apparatus. Either event can pull the tread stock and underlying belts out of alignment and, of course, subsequent stitching fixes these portions in such misaligned positions.
In the event that any of the aforementioned problems occur, their discovery prior to the curing process is preferable over discovery after the curing process, at final inspection. Before curing takes place, the tire is held together due primarily to the tacky nature of the materials used, and at that stage misaligned tread and/or belts may be physically removed from the tire carcass by peeling them away by hand. Should such a defect be discovered and so remedied, the basic carcass may be so salvaged by replacement of the misaligned tread and/or belts. A significant cost savings is therefore realized, and the problem of disposing of defective tires is reduced.
What is needed, therefore, is means for easily and reliably detecting improper placement of the tread stock prior to curing of the assembled tire. This means should not, add to the operation necessary to assemble, stitch or cure the tire.